Spin-Orbit Based Coherent Spin Ratchets

TL;DR

This paper investigates a quantum spin ratchet mechanism driven by spin-orbit interaction in mesoscopic systems, demonstrating its robustness against disorder and showing that increasing channels enhances spin transmission linearly.

Contribution

It extends a minimal spin ratchet model to include disorder and self-consistent charge redistribution, providing a more realistic analysis of the quantum spin ratchet in mesoscopic structures.

Findings

Spin ratchet mechanism is robust against disorder.

Multi-channel systems increase dc spin transmission linearly.

The model remains effective in the nonlinear adiabatic regime.

Abstract

The concept of ratchets, driven asymmetric periodic structures giving rise to directed particle flow, has recently been generalized to a quantum ratchet mechanism for spin currents mediated through spin-orbit interaction. Here we consider such systems in the coherent mesoscopic regime and generalize the proposal of a minimal spin ratchet model based on a non-interacting clean quantum wire with two transverse channels by including disorder and by self-consistently treating the charge redistribution in the nonlinear (adiabatic) ac-driving regime. Our Keldysh-Green function based quantum transport simulations show that the spin ratchet mechanism is robust and prevails for disordered, though non-diffusive, mesoscopic structures. Extending the two-channel to the multi-channel case does not increase the net ratchet spin current efficiency but, remarkably, yields a dc spin transmission increasing linearly with channel number.